1. Field of the Invention
The present invention relates generally to a method and apparatus for lining a host pipe, such as a steel pipe, with a synthetic liner, the liner being cooled to a very low temperature prior to insertion within in the host pipe to facilitate the insertion operation.
2. Description of the Prior Art
Fluid-carrying pipes are often subject to corrosion and other conditions which are detrimental to the life of the pipe, or to the fluids moving through the pipe. Plastic inserts have been used in the past for protective purposes but generally involve cumbersome and difficult procedures for effectively installing such liners, and particularly in sealing them to the wall of pipe.
U.S. Pat. No. 3,494,813, to Lawrence et al, Feb. 10, 1970, shows a method for installing a plastic liner in a pipe by using vacuum to draw the liner into the pipe and to assure tight sealing engagement between the liner and the pipe wall.
U.S. Pat. No. 1,708,141, to Kepler, Apr. 9, 1929, shows a method of lining a pipe with an elastomeric lining in which the lining is pushed through a reducing die and coated with cement.
U.S. Pat. No. 3,462,825, to Pope et al, Aug. 26, 1969, shows a method for lining a host pipe with a fluorocarbon liner. The liner is placed in the host pipe by gripping one end of the liner and pulling it through a reducing die and into the host pipe. The liner is then released, allowing it to expand into engagement with the inner wall of the host pipe.
Although certain of the above methods have attempted to install synthetic liners within tubular conduit without the use of heat, adhesives or vacuum, these methods have generally suffered from various deficiencies. One problem encountered in installing a downsized liner within a host pipe was maintaining the downsized liner at the downsized dimensions during the installation procedure since the downsized liner tended to reversely expand with time. Also, where a length of liner was pulled by a leading end during the installation, the liner tended to elongate and become thinner in sidewall cross-section at the leading end. The decrease in tensile strength which resulted, limited the distance the liner could be pulled without undue elongation and wall thinning distortion or severing.
An object of the present invention is to provide an improved synthetic liner for a host pipe in which the liner is firmly held in position within the host pipe by reason of radial pressure exerted on the host pipe by the synthetic liner.
Another object of the invention is to provide a method for installing a liner within a host pipe which places the liner in a condition of circumferential compression to thereby secure the liner within the surrounding host pipe.
Another object of the invention is the provision of a liner for a host pipe which is installed without the necessity of heating the liner with the risk of imparting thermal stresses to the liner.
Another object of the invention is to provide a method for lining a host pipe without the use of chemical bonding agents which, on occasion, fail to provide uniform bonding of the liner to the surrounding host pipe.
Another object of the invention is to provide an improved method for installing a liner within a host pipe in which the liner is cryogenically cooled to a supercooled state to facilitate insertion of the liner within the host pipe.
Another object of the invention is to provide a method for installing a liner by pulling the liner within a host pipe in which the tensile strength of the liner is increased by the method to allow the liner to be pulled over greater lengths.